Conventionally, it was difficult that a person performing inspection such as a medical doctor accesses a person under inspection during image taking with an MRI device, therefore, the so called Interventional Radiology (hereinafter, simply called as IVR) was as well as difficult.
For example, JP-A-7-106153 (1995) entitled “C Type Super Conducting Magnet” discloses a conventional art for avoiding the above problems.
The above referred to device takes MRI images after inserting a patient between two magnetic poles.
This device is for generating a uniform magnetic field by optimizing the configuration of the magnetic poles, however, because of weight limitation thereof, a uniform magnetic field space which can be used merely for inspecting a head portion of the patient is generally created.
However, in a case of whole-body use MRI device which permits an image taking of such as the abdomen, the chest and the bi-shoulder of a patient representing an inspection object without moving the patient during image taking, it is generally necessary to generate a uniform magnetic field with intensity variation of a few ppm (for example 2˜3 ppm) in an image taking region covered by a sphere having a diameter from 40 cm to more than 50 cm. Accordingly, it is required to develop an MRI device having a magnet which can generates a uniform magnetic field with its intensity variation of a few ppm (for example, 2˜3 ppm) in an image taking region covered by a sphere having a diameter from 40 cm to more than 50 cm while keeping a highly open space feeling in the magnet for an MRI device.
As has been explained above, it was difficult until now to generate a uniform magnetic field over a broad region in a magnet having a broad opening which gives an open space feeling for a person to be inspected (a patient) representing a measurement (image taking) object. Further, there is a problem to have to increase the outer diameter of the magnet in order to obtain a broad uniform magnetic field space, which causes other problems to deteriorate the open space feeling for the patient and easy access thereto. Still further, when it is intended to enlarge the uniform magnetic field region, which causes a problem of increasing the manufacturing cost of the magnet because the absolute value of magnetomotive forces of coils constituting the magnet has to be increased.
Further, JP-A-3-141619 (1991) discloses a magnet for generating a uniform magnetic field in a broad region in which currents in opposite directions are flown through two coils disposed in outside and inside along a same axis to generate magnetic fields in opposite direction and to superposed the same each other, thereby, a non-uniformity of magnetic field produced by a single coil is canceled out to enlarge a uniform magnetic field region.
Further, JP-A-9-153408 (1997) applied by the present applicants discloses a super conducting magnet device each of a pair of static magnetic field generation sources disposed in vertical direction so as to oppose each other is constituted so as to include one main coil unit for generating static magnetic field and a plurality of coil units for correcting irregular magnetic field, however, JP-A-9-153408 (1997) does not disclose specifically the DC current flow direction in these two sorts of unit coils.